1. Field of the Invention
The present invention relates generally to an apparatus for controlling a generator, the generator being directly coupled to, e.g., a gas turbine engine.
2. Description of the Background Art
A previously proposed control apparatus for an AC generator is exemplified by an Operation Manual of Honda EX 300 published by Honda Giken Kogyo, Company Limited in 1991.
In the above-identified Operation Manual, the generator is directly connected to a reciprocating engine, a thyristor-type inverter receiving three-phase voltages generated on respective windings of the generator and inverting them into a single phase rectangular wave AC voltage having a frequency of 50 Hz. An electrical load is connected to an AC receptacle across which the single phase rectangular wave AC voltage appears.
In the above-described configuration, it is not necessary to revolve the reciprocating engine at a rated revolution speed of the generator even when such a low load as only connecting a small electrical load is applied which has a power smaller than a rated power. This is because the continued revolution of the engine at the rated revolution speed means a wasteful consumption of engine fuel.
Therefore, a manual mode switch to select either a high load mode or a low load mode is installed on an external of a controller. When the low load mode is selected, a revolution speed control is carried out by the controller according to the electrical load. With no electrical load, the engine is held in a low-speed idling state. The controller controls the revolution speed of the engine so that the revolution speed becomes higher than the idling speed according to-the electrical load only when the electrical load is applied, thereby suppressing the wasteful fuel consumption.
If an excessive current flows in a case of the high load mode in which the engine (internal combustion engine) is always revolved at a rated revolution speed, the inverter is interrupted. If a load current exceeding rated powers flowed (both rated output powers of the engine and inverter), the engine revolution speed would become low and the inverter would possibly burn out due to temperature rises of switching elements (thyristors) with the inverter. To prevent such burn out the components of the inverter and lowered engine revolution speed, an output (current) of the inverter is detected so that when an excessive current above a predetermined value flows, the operation of the inverter is halted.
However, in the case of the low electrical load mode, the engine and inverter can only cope with the electrical load up to about 1/3 a rated load. Therefore, when a load exceeding about 1/3 the rated load (for example, the rated load) is abruptly applied with the engine being idle, the engine becomes under an excessive load state and stalls. To prevent such engine stalling, the mode switch needs to manually be switched to the high load mode. This is because the detection of the excessive current is determined with reference to the same set value of the excessive current as that in the case of the high load mode. Therefore, the inverter would not interrupted in the case of the low load mode.